Parameters of fluid media, i.e., of gases and/or liquids, for example, must be measured in different industrial fields. Parameters of this type include, for example, a pressure, a temperature, a flow velocity, a density, or similar physical and/or chemical properties or parameters of the fluid medium.
One important exemplary application of sensors of the above-mentioned type are pressure and temperature sensors for air conditioning systems. In air conditioning systems, the heat of evaporation of a coolant is normally used for cooling air (or another medium to be cooled). The coolant is then compressed in a compressor and thus liquefied. The coolant is heated when compressed. The absorbed heat is usually dissipated into the environment again in a gas cooler. The compression operation with the aid of the compressor must usually be controlled in such a way that the operating pressure does not exceed a predefined maximum pressure and the operating temperature does not exceed a predefined maximum temperature. For this purpose, pressure and temperature must be detected. In addition to this exemplary application in air conditioning systems, numerous other exemplary applications of sensors, in particular of pressure and temperature sensors, are known from various fields of the natural sciences and engineering sciences, in particular in process engineering and the automotive industry.
The use of two separate sensors for detecting pressure and temperature represents a considerable degree of complexity, since at least two plugs and several cable bundles must be available. Furthermore, the use of a plurality of individual sensors results in a plurality of sealing points at the interfaces and points of connection between the individual components. Therefore, an effort is made to obtain both pressure and temperature signals via a combined pressure and temperature sensor. Combined pressure and temperature sensors of this type are discussed in EP 1521 061 A2, DE 101 09 095 A1, DE 197 45 244 A1, and EP 0 893 676 A2. EP 1518 098 B1 discusses a similar sensor, which, however, is designed as a pure high-pressure sensor.
For future air conditioning systems used in motor vehicles, conventional R134a air conditioning systems are expected to be replaced by CO2 air conditioning systems, since according to the EU legislation, the coolant R134a previously used in air conditioning systems will be completely prohibited starting in the year 2016. In CO2 air conditioning systems of this type, increased operating pressures and temperature loads occur compared to conventional air conditioning systems, which place completely novel demands for the pressure and temperature loads of the components and sensors. Thus, pressures of up to 140 bar and medium temperatures of up to 180° C. occur during operation. Regarding hermeticity of the systems, leakages of less than 1 g per year are typically required.
The sensors known from the related art often have sealing surfaces and/or other sealing devices for sealing a sensor. The sensors are usually provided with threaded pieces, with the help of which the sensors may be threaded into a housing which receives the fluid medium. In many cases, flattenings are provided on the threads of the threaded pieces which are used as blow-out grooves and facilitate the threading of the sensor into the housing.
These flattenings on the threads have, however, the disadvantage that liquid and/or gaseous corrosive media from the environment may reach the sealing surface via these flattenings. For example, sensors of this type may be used in the engine compartment, so that oils, fats, engine cleaning agents, battery acid, and other types of impurities, which may occur in the surroundings of the engine, may reach and damage the sealing surface, thus reducing the reliability of the seal over the period of operation.